docs: def cotopics(model, threshold=None, **kwargs):
      """
      Two topics are coupled if they occur (above some ``threshold``) in the same
      document (s).
  
      Parameters
      ----------
      model : :class:`.LDAModel`
      threshold : float
          Default: ``2./model.Z``
      kwargs : kwargs
          Passed on to :func:`.cooccurrence`\.
  
      Returns
      -------
      :ref:`networkx.Graph <networkx:graph>`
  
      """
      if not threshold:
          threshold = 2./model.Z
  
      select = lambda f, v, c, dc: v > threshold
      return cooccurrence(model.corpus, 'topics', filter=select, **kwargs)